This project is a genetic analysis of Drosophila melanogaster DNA-dependent RNA polymerases. The objectives are as follows: 1) to gain an understanding of how eukaryotic RNA polymerases are involved in the regulation of gene transcription during development; 2) to determine how the intracellular concentration of the different forms of eukaryotic RNA polymerases is regulated; 3) to determine how the activities of these enzymes are modulated in different cell types and under different physiological conditions. The approaches to be used are: (1) screening temperature sensitive X-chromosome mutants for heat sensitive RNA polymerases. Conventional methods of inducing X chromosome ts mutants, using EMS mutagenesis, will be used. Each ts mutant will be screened biochemically by the methods I have previously developed. (2) Chromosomes from wild populations or from existing laboratory stocks will be screened for loci coding for heat sensitive or electrophoretic alleles of RNA polymerase II subunits. (3) The amanitin resistant mutants I have recovered will be further analyzed. (4) Genetic and biochemical analysis of a stock of flies (TM3/G1), which may have a heat resistant allele of one of the subunits of RNA polymerase II will be analyzed further.